The coat protein of the coliphage M13 is an integral membrane protein at all stages of viral infection. Our recent studies have established the orientation of this protein in the membrane and have duplicated this orientation in a simple in vitro model membrane assembly reaction. Studies have now begun to determine if the cell orients proteins in the membrane by the same means used in the model assembly reaction, i.e., as a response to the different lateral compressibility of the two halves of the bilayer resulting from membrane curvature.